The present invention relates generally to turbine engines and more particularly to methods and apparatus for securing airfoils used within turbine engines.
At least some known turbine rotor assemblies include a rotor wheel to which a plurality of rows of airfoils are coupled. The airfoils are arranged in axially-spaced stages extending circumferentially around the rotor. Each stage includes a set of stationary airfoils or nozzles, and a set of cooperating rotating airfoils, known as buckets.
Each bucket includes a dovetail that is used to couple the bucket to a matching dovetail slot defined by the rotor wheel. More specifically, each dovetail includes a recessed portion, known as a hook, that is defined by axial tangs, and that enables each airfoil to be slidably coupled to the machined rotor wheel dovetail.
Each rotor wheel dovetail slot is defined by a pair of parallel lands that are machined as part of the slot. During assembly, several bucket dovetails are inserted onto the dovetail lands through a loading slot defined within the rotor wheel dovetail groove lands. The closure bucket is then into the loading to provide a stabile surface to allow coupling of the bucket dovetail to the dovetail lands against the crushing surfaces. Once several buckets are coupled into the proper location, the locking bucket is removed. The coupled buckets now provide the stabile surface for additional buckets. Adjacent buckets are coupled to the rotor wheel through the loading slot and slid circumferentially into position and secured in place with a mounting pin. All of the buckets, with the exception of the closure bucket, are coupled to the rotor wheel by the machined lands.
In operation, the buckets are urged in the radial direction by the centrifugal force induced during rotation, and are also urged in the tangential direction by the aerodynamic force exerted on them by fluid flow. The dovetail tangs of the bucket cooperate with the rotor wheel lands by contact at the crushing surfaces to facilitate preventing movement of the buckets in the radial and tangential directions. However, because the closure bucket is positioned in the loading slot, the land portion of the wheel dovetail does not inhibit radial movement of the closure bucket and as such, it is necessary to restrain the closure bucket in the radial direction to prevent the closure bucket from being released from the loading slot during operation. Known closure buckets are coupled in position by a pair of grubscrews, which are inserted between the closure bucket and the circumferentially adjacent buckets. Inserting known grubscrews can be a time-consuming and laborious task that may require a relatively large machining station, such as a horizontal boring mill. During insertion of the grubscrews localized stress may be induced to the rotor assembly. Furthermore, if maintenance is required, removing the closure bucket may also be very time-consuming and requires the removal of a material peaned over the pins.
In one aspect, a method of assembling a turbine is provided. The method comprises coupling at least one bucket including an upstream side, a downstream side, an airfoil and a dovetail, to a rotor wheel. The method also comprises fixedly securing at least one bucket to the rotor wheel with a locking pin that extends from the bucket upstream side through the bucket dovetail to the downstream side.
In another aspect, a rotor assembly for a turbine is provided. The rotor assembly includes a plurality of buckets secured to a rotor wheel. Each bucket includes an upstream side, a downstream side, an airfoil, and a dovetail. Each airfoil extends from each dovetail. The plurality of buckets include at least a first bucket and at least a second bucket. At least one locking pin secures the at least one first bucket to the rotor wheel and extends from the upstream side of the bucket through the bucket dovetail to the downstream side of the bucket.
In a further aspect, a turbine including at least one rotor assembly is provided. The rotor assembly includes at least one rotor wheel and a plurality of buckets secured to the rotor wheel. Each bucket includes an upstream side, a downstream side, an airfoil and a dovetail. The airfoil extends radially from the dovetail. The plurality of buckets include at least one first bucket and at least one second bucket. At least one locking pin secures the at least one first bucket to the rotor wheel such that the locking pin extends from the bucket upstream side through the bucket dovetail to the bucket downstream side.